Rolling mill and method of using the same

Abstract

A work roll cross type rolling mill comprises a pair of work rolls and a pair of back-up rolls for backing up the work rolls. The back-up rolls are so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions. The work rolls are allowed to be inclined within horizontal planes with respect to the back-up rolls such that the axes of the work rolls cross the axes of the associated back-up rolls and cross each other. The nip between each the work roll and the associated back-up roll is lubricated so as to reduce axial thrust generated therebetween due to the crossing of the rolls. The cross angle between the work rolls is set and controlled during rolling operation only when the roll peripheral speed or the rolling speed is 50 m/min or higher. Advantages of work roll cross type rolling mill are fully extended to realize stable rolling without trouble so as to ensure high quality of the rolled product while achieving higher rate of operation of the mill with facilitated operation.

What is claimed is: 
     
       1. A rolling mill comprising: a pair of work rolls;   a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions;   means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other;   means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; and   cross angle setting and controlling means for performing setting and control of the cross angle between said work rolls during rolling operation only when the roll peripheral speed or the rolling speed is above a predetermined minimum value.   
     
     
       2. A rolling mill according to claim 1, wherein said predetermined minimum value is 50 m/min. 
     
     
       3. A rolling mill according to claim 1, further comprising interlocking means which prevents said cross angle setting and controlling means from performing the setting and control of said cross angle between said work rolls when the roll peripheral speed or the rolling speed is below said predetermined minimum value. 
     
     
       4. A rolling mill according to claim 3, wherein said predetermined minimum value is 50 m/min. 
     
     
       5. A rolling mill according to claim 1, wherein said cross angle setting and controlling means sets and controls the angles of said axes of said work rolls in counter directions to each other with respect to a line which is perpendicular to the direction of rolling, within a range of from 0° to 2.5° in accordance with the rolling conditions. 
     
     
       6. A rolling mill according to claim 1, further comprising a work roll thrust plate associated with each said work roll so as to bear a thrust acting on said work roll, a hydraulic cylinder for supporting said work roll thrust plate, and work roll cross angle adjusting means which adjusts the cross angle between said work rolls so as to reduce the thrust when the level of the thrust supported by said hydraulic cylinder has become excessively large. 
     
     
       7. A rolling mill according to claim 1, wherein a work roll bending force or a work roll balance force of 50 tons/chock or greater is applied to said work rolls. 
     
     
       8. A rolling mill according to claim 1, further comprising thrust measuring means for measuring the level of the thrust acting on said back-up roll and said work roll due to crossing of said back-up and work rolls, and rolling load difference compensating means for compensating, based on the thrust level measured by said thrust measuring means, for influence of the roll crossing on the difference in the rolling load appearing between the driving end and the operation end of said rolls. 
     
     
       9. A rolling method for rolling a material by a rolling mill of the type which includes: a pair of work rolls; a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions; means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other; and means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; said method comprising: conducting setting and control of the cross angle between said work rolls during rolling operation only when the roll peripheral speed or the rolling speed is above a predetermined minimum value.   
     
     
       10. A rolling method according to claim 9, wherein said predetermined minimum value is 50 m/min. 
     
     
       11. A rolling method according to claim 9, wherein the setting and control of said cross angle between said work rolls is prohibited when the roll peripheral speed or the rolling speed is below said predetermined minimum value. 
     
     
       12. A rolling method according to claim 11, wherein said predetermined minimum value is 50 m/min. 
     
     
       13. A rolling method according to claim 9, wherein the setting and control of the angles of said axes of said work rolls are performed in counter directions to each other with respect to a line which is perpendicular to the direction of rolling, within a range of from 0° to 2.5° in accordance with the rolling conditions. 
     
     
       14. A rolling method according to claim 9, wherein said rolling mill further includes a work roll thrust plate associated with each said work roll so as to bear a thrust acting on said work roll, a hydraulic cylinder for supporting said work roll thrust plate, said method further comprising adjusting the cross angle between said work rolls so as to reduce the thrust when the level of the thrust supported by said hydraulic cylinder has become excessively large. 
     
     
       15. A rolling method according to claim 9, wherein a work roll bending force or a work roll balance force of 50 tons/chock is applied to said work rolls in the period between the clearance of the work rolls by the trailing end of a preceding rolled material and catching of the leading end of the next material to be rolled, thereby preventing slip between said work roll and the associated back-up roll due to deceleration of the rolls. 
     
     
       16. A rolling method according to claim 9, further comprising measuring the level of the thrust acting on said back-up roll and said work roll due to crossing of said back-up and work rolls, and effecting, based on the measured thrust level, compensation for influence of the roll crossing on the difference in the rolling load appearing between the driving end and the operation end of said rolls. 
     
     
       17. A method of using a rolling mill of the type which includes: a pair of work rolls; a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions; means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other; and means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; said method comprising: using said rolling mill as a rough rolling mill while setting the maximum allowable rolling load to 6000 tons, and setting a cross angle between said work rolls above zero when said rolling load is lower than or equal to said maximum allowable rolling load and setting the cross angle between said work rolls to zero when said maximum allowable rolling load is exceeded. 
     
     
       18. A method of using a rolling mill of the type which includes: a pair of work rolls; a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions; means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other; and means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; said method comprising: using said rolling mill as a finish rolling mill while setting the maximum allowable rolling load to 5000 tons, and setting a cross angle between said work rolls above zero when said rolling load is lower than or equal to said maximum allowable rolling load and setting the cross angle between said work rolls to zero when said maximum allowable rolling load is exceeded. 
     
     
       19. A method of using a rolling mill of the type which includes: a pair of work rolls; a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions; means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other; and means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; said method comprising: using said rolling mill as a thick-sheet rolling mill while setting the maximum allowable rolling load to 10000 tons, and setting a cross angle between said work rolls above zero when said rolling load is lower than or equal to said maximum allowable rolling load and setting the cross angle between said work rolls to zero when said maximum allowable rolling load is exceeded. 
     
     
       20. A method of using a rolling mill of the type which includes: a pair of work rolls; a pair of back-up rolls for backing up said work rolls, said back-up rolls being so arranged that their axes can be inclined within horizontal planes only to three or four specific angular positions; means for allowing said work rolls to be inclined within horizontal planes with respect to said back-up rolls such that the axes of said work rolls cross the axes of the associated back-up rolls and cross each other; and means for providing lubrication between each said work roll and the associated back-up roll so as to reduce axial thrust generated therebetween due to the crossing of the rolls; said method comprising: using said rolling mill as a cold rolling mill while setting the maximum allowable rolling load to 3500 tons, and setting a cross angle between said work rolls above zero when said rolling load is lower than or equal to said maximum allowable rolling load and setting the cross angle between said work rolls to zero when said maximum allowable rolling load is exceeded.